Now, if you're wondering how to get the big icons up on the wiki, this is a how to guide to help you out.
Go to the finder and locate the application you want to get the icon off
Right click (or ctrl and click) on it and select "Get Info"
Click on the icon so it gets highlighted at the top left of the new window/inspector.
Go to Edit->Copy
Open Preview (Applications folder)
On Preview's menu go to File->New from clipboard. This will open it up
Make sure the biggest icon is selected. Now go to File->Save as
Save it as a PNG file somewhere. It is now ready to upload